1. Field of the Invention
The present invention relates to exposure control systems for photographic apparatus, in general, and to the control of the shutter blades in an exposure control system of a single lens reflex camera, in particular.
2. Description of the Prior Art
Photographic cameras of the reflex type have been developed wherein the exposure of photosensitive material within the camera is both automatically and electronically controlled. Such cameras are often of the single lens reflex variety and require a complex exposure control system in order to accommodate a requisite viewing or viewing and focusing mode. During this mode of operation the single lens reflex camera is in a normally open status wherein a shutter mechanism that forms a portion of the exposure control system allows or unblocks the passage of scene light through an exposure opening or taking lens to a viewfinder.
At the commencement of an exposure cycle, the shutter mechanism of the camera exposure control system is driven into a closed or light blocking orientation whereupon the photographic camera is automatically operated to change from the viewing or viewing and focusing mode to an exposure mode in which photosensitive film is made accessible to the optical path of the taking lens of the camera.
In one type of single lens reflex camera employing a shutter mechanism of the "scanning" blade type, such as that described in U.S. Pat. No. 3,672,281 to E. H. Land, when the camera has assumed the exposure mode of operation, the exposure control system operates to release a shutter mechanism from its light blocking orientation where such exposure control parameters as exposure interval and aperture size are controlled as a function of scene brightness as evaluated with respect to the sensitometric characteristics of the film being exposed. At the termination of the electronically determined exposure interval, the shutter is again driven to a fully closed or light blocking position to terminate exposure until such time as the camera reassumes the viewing or viewing and focusing mode.
The actuation of the exposure control system to drive the shutter mechanism from its light unblocking orientation to its light blocking orientation at the commencement of an exposure cycle and prior to an exposure interval produces a considerable amount of mechanical noise that is often distracting to the subject being photographed. A subject within a scene hearing the mechanical noise generated by the shutter mechanism at this point in the exposure cycle will often incorrectly conclude that this particular noise indicates that exposure is complete and start moving during the subsequent exposure, thereby causing a blurred image to result.
An example of an exposure control system operated in this manner is described in U.S. Pat. No. 3,942,183 to Whiteside. In this Whiteside patent a pair of overlapping "scanning" type shutter blade elements are supported within a camera housing in a light path between a taking or objective lens and photosensitive film located at the camera's focal plane. A pair of scene light admitting primary apertures are respectively provided in the blade elements to collectively define a progressive variation of effective aperture openings in accordance with longitudinal and lateral displacement of one blade element with respect to the other blade element.
A tractive electromagnetic device in the form of a plunger-type solenoid is employed to displace the shutter blades with respect to each other. The solenoid is of conventional design having an internally disposed cylindrical plunger unit which retracts inwardly into the body of the solenoid upon energization thereof. The solenoid plunger is suitably coupled to each shutter blade element such that, upon energization, the solenoid actuates the shutter mechanism to its fully closed position. A subject distracting mechanical noise is generated when the solenoid plunger is retracted into its seated position within the solenoid body by the solenoid drive system.